anti-Markovnikov addition of tellurium tetrachloride to trimethyl ethynyl silane

Journal of Organometallic Chemistry 693 (2008) 2509–2513

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anti-Markovnikov addition of tellurium tetrachloride to trimethyl ethynyl silane S.V. Amosova *, A.V. Martynov, V.A. Shagun, M.V. Musalov, L.I. Larina, L.B. Krivdin, L.V. Zhilitskaya, M.G. Voronkov A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 1, Favorsky Street 664033, Russia

a r t i c l e

i n f o

Article history: Received 27 February 2008 Received in revised form 15 April 2008 Accepted 28 April 2008 Available online 6 May 2008 Keywords: anti-Markovnikov addition Ethynyl silane Tellurium tetrachloride Multinuclear NMR spectroscopy Quantum-chemical calculations

a b s t r a c t An investigation of the TeCl4 interaction with trimethyl ethynyl silane 1 in CHCl3 has shown that antiMarkovnikov adduct [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium trichloride is formed as the only product. In time, it is hydrolyzed to give [Z-1-(trimethylsilyl)-2-chlorovinyl]tellurium (hydroxy) dichloride which, in turn, is dehydrated to afford bis[(2-chloro-1-trimethyl-silylvinyl)dichlorotellurium]oxide. These data revealed that the reaction studied was the first example of anti-Markovnikov syn-addition of TeCl4 to terminal acetylenes. A computed simulation of the TeCl4 interaction with ethynyl silane 1 in a gas state using PES method did not reveal dominating orientation of the addition but showed the conditions at which anti-Markovnikov addition can occur and which were probably met in carrying out the reaction in CHCl3. Ó 2008 Elsevier B.V. All rights reserved.

1. Introduction It is known that interaction of tellurium tetrachloride or aryltellurium trichloride or tribromide with alkynes RC„CR1 (R = Ph, CH2OH; R1 = H, Alk, Ph) in apolar solvents (CCl4, CHCl3, C6H6) proceeds regio- and stereoselectively to furnish Z-RCCl@C(R1)TeCl3 [1a,1b,1c,1d,1e,1f,1g,1h,1i,1j]. The interaction of TeCl4 and TeBr4 with twofold excess of terminal acetylenes RC„CH (R = Ph, C5H11) in benzene under reflux leads to formation of the 1:2 adducts – bis(a-organoyl-b-halogenovinyl)tellurium dichlorides (RCX@CH)2TeX2 (X = Cl, Br) [1h,2a,2b]. When polar solvents (MeOH) are used, the reaction of aryl tellurium tribromides with terminal alkynes and phenylacetylene shows the same regioselectivity, but in this case E-isomers of monoadducts are formed due to anti-addition [1d]. In the reactions of TeBr4 [2a,2b] and aryl tellurium tribromides [2b] with alkynes in benzene, anti-addition along with the syn-addition is realized, thus affording the mixtures of Zand E-isomers of the corresponding adducts. It should be emphasized that these addition reactions obey the Markovnikov rule. The reactions of tellurium tetrahalides with ethynyl silanes (silicon analogs of terminal alkynes) were unknown to date. Earlier, we have found a new cyclization reaction of TeCl4 with diorganyl diethynyl silanes resulting in a new class of unsaturated silicon– tellurium containing heterocycles – 4,4-diorganyl-1,1,3,6-tetrachloro-1,4-tellurasilafulvenes [3]. To explain the formation of these heterocycles we have suggested that the anti-Markovnikov syn-

* Corresponding author. E-mail address: [email protected] (S.V. Amosova). 0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2008.04.041

addition of TeCl4 to ethynyl moiety of diethynyl silane occurs in the first stage of the reaction. Since the anti-Markovnikov orientation of the addition to acetylenic systems in a case of TeCl4 is yet unknown, in this work we have computed probabilities of the Markovnikov and anti-Markovnikov modes of the TeCl4 addition to trimethyl ethynyl silane, thus simulating a first stage of the aforementioned reaction, and then studied the interaction of TeCl4 with Me3SiC„CH. 2. Results and discussion 2.1. Quantum-chemical simulation of the reaction To elucidate the most possible direction of TeCl4 addition to acetylenic moiety of trimethyl ethynyl silane 1 quantum chemical computations of the formation routes for the Markovnikov (a-) 2 and anti-Markovnikov (b-) 3 addition products were carried out (Scheme 1). For this purpose, within the framework of the molecular simulation methods we have investigated the potential energy surface (PES) of the mechanisms of interaction of 1 with TeCl4 in order to choose the reaction channel that probably depends, first of all, on the topological and stereoelectronic characteristics of the pre-reaction bimolecular complex 1-TeCl4. Critical points and gradient channels connecting them were found using the density functional theory (DFT) with the threeparameter functional B3LYP [4a,4b,4c]. Taking into consideration the character of the electron shells of the atoms included into the systems under study, the basis set LANL2DZ was employed. Geometry full optimization of the molecular systems was carried

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Me3Si

H C=C

Cl

Structure

CH + TeCl4

Me3SiC

TeCl3

Table 1 Total energy ( Etot, a.u.)a, zero-point vibration energies (ZPVE, a.u.), relative energies (DE, kJ/mol), virtual and the lowest harmonic frequencies ((ix/x1, cm 1) and dipole moments (l, D)

2

1 Me3Si

H C=C

Cl3Te

Cl 3

Scheme 1.

out till the value of 10 5 a.u./Bohr. On analyzing flat sites of the PES the gradient value has been installed at the level of 10 6 a.u./Bohr. Stationary points were identified by the analysis of the Gesse matrix. Search and localization of the transition states (TS) were carried out by method of linear and square-law synchronous transit QST2 and QST3 [5]. Analysis of the vibration frequencies in the Saddle point was performed, and conformity of the critical points with the gradient line connecting them was proved by the interior reaction coordinate method (IRC). All calculations were conducted using program complex GAUSSIAN-98 [6]. To examine the interaction of 1 with TeCl4 as well as localize critical points corresponding to the most stable pre-reaction complexes, there have been computed the optimal structures of the isolated parent compounds used as starting materials for designing the bimolecular states. The basic geometrical and energy characteristics of the isolated ethynyl silane 1 and TeCl4 are given in Fig. 1 and Table 1. Tellurium tetrachloride is represented according to the terminology of inorganic stereochemistry [7] as Te(monodental ligand)3(LEP) and is capable of self-stabilizing in the configuration of both trigonal pyramid (T) with LaTeLe equal to 91.2° (Fig. 1) which is close to the experimental values in RTeL3 (for instance, R4BTeMe3 – 91.3° [8]), or square pyramid (S). The computations have shown insignificant (0.2 kcal/mol) predominance of the T-configuration (Table 1). Stabilization of TeCl4 and formation of

TeCl4(T) TeCl4(S) 1 (1-TeCl4)1 (K1) (1-TeCl4)2 (K2) (1-TeCl4)3 (K3) (1-TeCl4)4 (K4) TS1 (K2,K4 ? 2) TS2 (K1 ? 2) TS3 (K1 ? 3) 2 3 a

Etot 67.83435 67.83425 200.38911 268.22826 268.23897 268.23623 268.23772 268.21959 268.22253 268.21912 268.26888 268.27136

ZPVE

DE

x1

l

0.00353 0.00375 0.13219 0.13632 0.13709 0.13704 0.13675 0.13691 0.13688 0.13713 0.14000 0.13947

0.00 0.20 – 25.07 18.83 20.52 19.40 30.88 29.02 31.31 1.89 0.00

40 50 126 14 13 13 16 i181 i178 i172 31 19

1.43 1.84 0.63 2.25 5.50 6.12 5.32 7.04 9.13 8.22 4.08 5.21

1 a.u. = 627.506 kcal/mol.

the pre-reaction bimolecular complex on the interaction with silane 1 could occur with partial or complete reorganization of TeCl4 configuration. Formally, configurational state of the complex – Te (monodentant ligand Cl)3 (monodentant ligand silane 1) (LEP) – can represent the spectrum of T–S configurations [7]. The topology of the complex could drastically influence the mechanism of the addition reaction. The calculations performed and the PES analysis of the TeCl4 interaction with the acetylenic moiety of the ethynyl silane 1 allow us to localize four types of the complexes with different relative stabilities and probabilities of formation (Fig. 1, Table 2). The structures K1 and K4 are related to the T configuration, while K2 and K3 are assigned to the S configuration. The values of thermodynamic stabilities of the complexes obtained (estimated as a difference between total energies of the optimal states of the parent compounds and the product) are 3.01, 9.08, 8.08 and 8.95 kcal/mol for K1, K2, K3 and K4 states, correspondingly. The structure K3 falls down from the total scheme of the complexes discussed. Despite the probability of the realization of the concerted reaction of the product 3 formation via the four-centered transition state (TS), the PES analysis has shown that the depth

Fig. 1. Molecular structures and salient geometrical parameters of the compound 1 and TeCl4 and their bimolecular complexes (1-TeCl4)n. Bond lengths are in Å, bond angles – in grad.

S.V. Amosova et al. / Journal of Organometallic Chemistry 693 (2008) 2509–2513 Table 2 Spin–spin coupling constants 1JCH of the four possible isomers of 1-silyl-2-chlorovinyl tellurium trichloride calculated at the DFT-B3LYP/aug-cc-pVTZ-J/6-311G** levela Compound

JDSO

Z-H3SiC(TeCl3)@CHCl E-H3SiC(TeCl3)@CHCl E-H3SiCCl@CHTeCl3 Z-H3SiCCl@CHTeCl3

1.27 1.50 1.72 1.67

JPSO 0.36 0.45 0.35 0.45

JSD

JFC

J

Experiment

0.44 0.61 0.33 0.31

197.88 194.10 180.88 185.85

199.2 195.8 182.6 187.35

201.6b

a All couplings and their contributions are in Hz; Equilibrium HF/6-31G** geometries were used throughout. b Measured in compound 3.

of the potential well, where complex K3 is situated from the side of its possible transition to the more stable state K2, does not exceed 1.7 kcal/mol. The interconversion activation parameters of other computed complexes exceed 17 kcal/mol, which as will be shown below, surpass the activation barriers for the product 2 and 3 formation. The most stable is the square pyramid complex K2, where the interaction of TeCl4 with the p-system of the acetylenic moiety delivers the appreciable deformation of the valence angle CCH to 170.6°. Complex K2 through TS1 (Fig. 2) with the activation barrier 12.48 kcal/mol affords product 2. In the stationary state K4 that is slightly weaker in relative stability than complex K2 (0.57 kcal/ mol) transition to the product 2 occurs via the same transition state (TS1) with the activation barrier of 11.91 kcal/mol.

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All attempts to localize in the state K2 and K4 gradient channels leading to the anti-Markovnikov adduct 3 failed. The PSE analysis shows that in the less stable complex K1 realization of two independent gradient channels leading to the products 2 and 3 turns to be possible. Firstly, as a main component of the reaction coordinate in both channels, an interatomic distance between Cb atom and axial chlorine atom acts. In the next stage, the reaction channel is capable of shifting both to concerted or ionic addition. The former through TS2 results in the product 2, the latter through TS3 gives the product 3. Thus, formation of the anti-Markovnikov adduct 3 in the reaction directly relates to accumulation in the reaction mixture of sterically favorable bimolecular complexes from those considered above. Increase in the thermolysis rate probably shifts reaction channel towards ionic component, which results in a positive effect for the product 3 formation. It is necessary to note also, that formation of the compound 3 will take place on transition to a polar phase state, which is capable of increasing the stability of the complex K3 since a degree of its charge separation, judging by the values of dipole moments, is higher than in the complex K2 (Table 1). Based on slight distinction in relative stabilities of the complexes K2 and K3, complex K3 could become dominating, which also rises the probability of the adduct 3 formation. Thus, calculations made have not reveal dominating orientation of the addition in the reaction of TeCl4 with ethynyl silane 1, while in a gas phase a certain preference of the Markovnikov addition is observed.

Fig. 2. Molecular structures and salient geometry parameters of the addition reaction products (2 and 3) and transition states (TS1–3) connecting them with the parent complexes Kn. Bond lengths are in Å, bond angles – in grad.

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2.2. Experimental investigation of the reaction We have established that the interaction of tellurium tetrachloride with trimethyl ethynyl silane 1 in chloroform at room temperature is a first example of anti-Markovnikov syn-addition of TeCl4 to terminal acetylenes. As a result of this reaction, both in equimolar ratio of TeCl4 and Me3SiC„CH and in 1:2 ratio, a monoadduct – [Z-1-(thimethylsilyl)-2-chlorovinyl]tellurium trichloride 3 – is formed (Scheme 2). In the 1H NMR spectra, vinyltellurium trichloride 3 manifests itself as a low-field singlet signal of olefinic proton (@CH) at d 8.00 ppm (in CDCl3) (3JTe–H 28.2 Hz) and a singlet signal of trimethyl silyl group at d 0.54 ppm (CDCl3). The 13C NMR spectra are characterized by a doublet signal of sp2-hybridized carbon atom @CH at d 144.31 ppm (1JC–H 201.6 Hz), a singlet signal of @C(Si)Te at d 148.62 ppm and a quartet signal of Me3Si group at d 0.76 ppm (1JC–H 121.14 Hz), the 125Te NMR spectra show a signal at d 1407 ppm. In the 29Si NMR spectra the Me3Si group appears as a signal at d 7.3 ppm. The presence in 2D NOESY NMR spectra of the cross peaks, induced by the dipole–dipole interaction between @CH and methyl protons of Me3Si group, points to cis-arrangement of an olefinic proton and Me3Si group. Formation of the 1:1 adduct is supported by the elemental analysis data. In time, tellurium trichloride 3 is hydrolyzed on air to give [Z-1(trimethylsilyl)-2-chlorovinyl]tellurium(hydroxy) dichloride (4), which is registered in the 1H NMR spectra by a singlet signal of an olefinic proton at d 7.23 ppm (in CDCl3) and a singlet signal of Me3Si group at d 0.42 ppm. In the IR spectra of the product an intensive band of the OH group appears at m 3352 cm 1. In turn, due to intermolecular dehydration in chloroform the compound 4 turns into bis[(2-chloro-1-trimethylsilylvinyl)dichlorotellurium]oxide 5 within several hours (Scheme 3). Formation of the compound 5 is well explained by the common trend of diaryltellurium dichlorides and dibromides Ar1Ar2TeX2 to yield bis(diaryldihalogenotellurium)oxides (Ar1Ar2TeX)2O (X = Cl, Br) as a result of hydrolysis [9]. Bis(dichlorotellurium)oxide 5 manifests itself in the 1H NMR spectra by a high-field singlet signal of an olefinic proton at d 7.22 ppm (in CDCl3) (3JTe–H 24.7 Hz) and a singlet signal of the Me3Si group at d 0.49 ppm (CDCl3). In the 13C NMR spectra there are a doublet signal of @CH at d 133.13 ppm (1JC–H 206.8 Hz), a doublet signal of @C(Si)Te at d 157.21 ppm 2JC–H 15.1 Hz) and a quartet of the Me3Si group at d 0.23 ppm (1JC–H 121.3 Hz), in the

Me3Si CH + TeCl4

Me3SiC

H C=C

Cl3Te

1

Cl 3

Scheme 2.

Me3Si H2O, 20 h

Me3Si

H

H

2.3. Structure assignment of the reaction products by the fine structure of the 13C NMR spectra Comparison of the coupling constants of an olefinic proton and tellurium atom in the compounds 3 and 5 with the data for divinyl telluride [10a,10b] as well as the experimental value of 2JTe–H for Z2-chlorostyryl-1-tellurium trichloride obtained from the 1H NMR spectra of this compound, synthesized by us using the known reaction of TeCl4 with phenylacetylene [1a,1b,1c,1d,1e,1f,1g], does not allow to unambiguously judge about regio- and stereoisomerism of these compounds only on the basis of these spectral data. In particular, large difference in the values of the 2JTe–H constant for Z-2chlorostyryl-1-tellurium trichloride (5.6 Hz) and the 2JTe–H constant for divinyl telluride (48.8 Hz) almost coinciding with the trans-vicinal constant 3JTe–H (41.8 Hz) for the same compound, testifies to ambiguity of these values application to determine the isomerism of the unsaturated tellurium trichloride and dichloride 3 and 5 on the basis of fine structure of the 125Te or 1H spectra. In contrast, for similar selenium analogs the regularities associating the JSe–H constants with relative arrangements of the hydrogen and selenium atoms at a double bond have been found [11a,11b,11c,11d]. Choice in favor of the anti-Markovnikov structure of the compounds prepared was made on the basis of 1JCH experimental coupling constant of the compound 3 in comparison with the calculated values in the four possible isomers of the model compound – 1-silyl-2-chlorovinyl tellurium trichloride (Table 2). Calculations of the 1JCH were performed at the DFT-B3LYP level with the basis set aug-cc-pVTZ-J [13] including four tight s-functions for both hydrogen and carbon. All four non-relativistic coupling contributions were taken into account, namely, Fermi contact, JFC, spin–dipolar, JSD, diamagnetic spin–orbital, JDSO, and paramagnetic spin–orbital, JPSO. Calculations of spin–spin coupling constants have been carried out using the DALTON package [14] while geometrical optimizations were performed with the GAMESS code [15]. The calculations of 1JCH point to the large differences in the values of these coupling constants in relation to the electronegativity of the element (Cl 2.83, Te 2.01) attached to the coupled carbon atom as well as to the spatial arrangement of the adjacent substituents at the C@C bond giving rise to the unambiguous assignment of the anti-Markovnikov structure. Thus, the reaction of tellurium tetrachloride with trimethyl ethynyl silane represents the first example of unusual anti-Markovnikov addition of tellurium tetrahalide to terminal acetylenes.

3. Experimental

Cl

Cl2Te

3

Si NMR spectra – a signal at 6.44 ppm, in the 125Te NMR spectra – a doublet signal at d 1371.6 ppm (3JTe–H 21.8 Hz). In the IR spectra no absorption of the OH group is observed. As distinct from the IR spectra of the compounds 3 and 4, which are characterized by two strong absorption bands at m 1542–1547 and 1248– 1255 cm 1, the compound 5 in the same region shows four strong absorption bands: 1540, 1464, 1378 and 1254 cm 1. Elemental analysis of the compound 5 corresponds to the structure of bisZ,Z-[(2-chloro-1-trimethylsilylvinyl)dichlorotellurium]oxide.

3.1. General

O Cl

(HO)Cl2Te 4

- H2O Cl2Te

Cl

Me3Si

H 5

Scheme 3.

The 1H (400 MHz), 13C (100.6 MHz), 29Si (79.5 MHz) and 125Te (126.4 MHz) NMR spectra were taken in the CDCl3 solutions on a Bruker DPX-400 spectrometer. HMDS was used as an inner standard for the 1H NMR spectra; the 125Te NMR spectra were recorded relative to Me4Te. The IR spectra were recorded on a Bruker IPS 25 spectrometer. Trimethyl ethynyl silane 1 was prepared according to the procedure [12]. TeCl4 was obtained from Aldrich.

S.V. Amosova et al. / Journal of Organometallic Chemistry 693 (2008) 2509–2513

3.2. Interaction of trimethyl ethynyl silane 1 with TeCl4 at ratio 1:1 and 2:1 To TeCl4 (2.72 g, 10.1 mmol) in 10 ml CHCl3 was added in argon atmosphere ethynyl silane 1 (1.00 g, 10.1 mmol) in 10 ml CHCl3, the resulting mixture was stirred at 20 °C for 6 h in daylight. A dark gray inorganic deposit (Te, unreacted TeCl4) blurring on air was filtered off. After evacuation of the solvent from the filtrate was obtained 1.45 g (39%) of the product 3 as a white crystalloid matter, m.p. 80.5–81 °C. 1H NMR (CDCl3, 25 °C, d, ppm): 8.00 (s, @CH, 1H, 2 JSi–H 7.7 Hz, 3JTe–H 28.4 Hz), 0.54 (s, 9H, Me3Si, 4JTeH 10.6 Hz, 2 JSi–H 6.9 Hz); 13C NMR (CDCl3, 25°C, d, ppm): 144.3 (d, @CH, 1JCH 201.6 Hz), 148.6 (s, @C), 0.76 (q, CH3, 1JCH 121.1 Hz); 29Si NMR (CDCl3, 25 °C, d, ppm): 7.33s; 125Te NMR (CDCl3, 25 °C, d, ppm): 1317. IR (KBr) 3049 (@CH), 2940, 2902, 1547s, 1520w, 1413, 1283w, 1284s, 869s, 845s, 822, 764, 709, 630, 506, 415s cm 1. Anal. Calc. for C5H10SiTeCl4: C, 16.35; H, 2.74; Cl, 38.57; Si, 7.64; Te, 34.71. Found: C, 16.11; H, 2.52; Cl, 38.29; Si, 7.42; Te, 33.56%. Similarly, the product 3 in 35% yield was prepared by the reaction of equimolar mixture of TeCl4 and trimethyl ethynyl silane 1 in chloroform in argon atmosphere at darkness. Similarly, the product 3 in 50% yield was prepared in the reaction of TeCl4 and silane 1 in darkness at the reagent ratio 1:2, correspondingly. Similarly, from TeCl4 (0.94 g, 3.5 mmol) and silane 1 (0.34 g, 3.5 mmol) in 20 ml of CHCl3 after stirring for 2.5 h at 20 °C in argon atmosphere on daylight and keeping the solution overnight was obtained 0.31 g of the mixture of the compounds 3, 4 and 5 in ratio 1:10:10 (according to the 1H NMR data). Compound 4: 1H NMR (CDCl3, 25 °C, d, ppm): 7.24s (@CH), 0.42s(CH3). IR (Vasiline oil) 3352 (OH), 3011, 2959, 2930, 2902, 2855, 1541s, 1444, 1411, 1385, 1255s, 1216, 1050, 849s, 760s, 692s, 510, 446 cm 1. Compound 5: 1H NMR (CDCl3, 25 °C, d, ppm): 7.22s (@CH, 3JTeH 25.7 Hz, 1JCH 206.6 Hz), 0.49s (CH3, 2JSiH 6.9 Hz), 4JTeH 10.6 Hz); 13 C NMR (CDCl3, 25°C, d, ppm): 133.1d (@CH, 1JCH206.8 Hz), 157.2d (@C, 2JCH 15.1 Hz), 0.23q (CH3, 1JCH 121.3 Hz); 29Si NMR (CDCl3, 25 °C, d, ppm): 6.44; 125Te NMR (CDCl3, 25 °C, d, ppm): 1371.8d (3JTe–H 25.2 Hz). Similarly, from TeCl4 (1.69 g, 6.25 mmol) and silane 1 (1.23 g, 12.5 mmol) in 40 ml of CHCl3 in argon atmosphere at 20 °C after stirring in darkness for 11 h was obtained 1.39 g of the 1:3 mixture of the compounds 3 and 5 (according to the 1H NMR data). Recrystallization from chloroform/hexane (1:4) afforded compound 5 as white fine crystals, m.p. 154.5 °C. The 1H, 13C, 29Si, 125Te NMR see above. IR (vaseline oil) 3010, 2964, 2924, 2853, 1649, 1572, 1540, 1465, 1377, 1254, 887, 849, 827, 764, 738, 700, 626, 447 cm 1. Anal. Calc. for C10H20Cl6Te2Si2O: C, 17.65; H, 2.96; Cl, 31.27; Si, 8.26; Te 37.51. Found: C, 17.85; H, 3.26; Cl, 31.71; Si, 7.89; Te 37.67%. Acknowledgement Financial support of this work by the Presidium of Russian Academy of Sciences (Grant No. 8.19) is gratefully acknowledged.

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